There were already issues with the PS3 and the game with the current engine "which suprises me with the toosl claimed to be scalable). So the rewrite had to happen.
I am sure SE will do their best to make it function on the console with it's limited capabilities. No, it won't have the potential of the PC version, it simply lacks the memory, GPU/CPU combined power. As a result of bringign it to the PS3, load zones will return, but more variety to zones will accur.
Sure, the PS3 can pull off graphical tricks when a game has limited field of view and distance, but you often see now, sistance backgrounds are blurred and static. When it comes to an MMO, things change.
I have a PS3, Xbox 360 (which the unified memory has it's advantages-slightly) but I wouldn't play this on a console, even tho I use a contoroller.
On the bottlenecking topic. The ps3 is far more prone to it. Part of it is the Memory design, split design of it, and bottleneck and shiftign between the vram and main ram.
The cells, while good on paper, are bottlenecked by the memory and lack of it. As well as they must handle all audio encoding, system fuction, and OS. A PC today is not bottlenecked as much, not with the variosu cachign options, far more avaiable memory from the get go, and the option for far superior hard drives and access times.
Will FFXIV be as good on the PS3 as middle to high end PC's? No. Will it be so much worse that it isn't worth getting? No. They can have less detail and smooth out the images, but the main thing is stability of frame rate and gameplay.
SE stated the new engine will allow graphical quality on lower end systems and the PS3, while giving the option for higher detail on higher end PC's. Testures won't be as detailed. Bump mapping not very high, Anti Alaising probably very low (as it already is if you do not override it) but there are ways to improve the look without all that.
For peopel with out decent PC's it's a good option. Most probably it will not exceed 720p, medium testure quality, nor more then 30 fps. But still very playable.